doc improvement

[TravisDev]

added an example in the Parse.Object docs to show usage of saving a single attribute on a parse object. Users may use this in typescript class extensions of Parse.Object as a class attribute mutator.

[codecov]

Codecov Report

Merging #1349 (e324525) into master (16b45fd) will not change coverage.
The diff coverage is n/a.

❗ Current head e324525 differs from pull request most recent head b09b256. Consider uploading reports for the commit b09b256 to get more accurate results

@@           Coverage Diff           @@
##           master    #1349   +/-   ##
=======================================
  Coverage   99.23%   99.23%           
=======================================
  Files          60       60           
  Lines        5920     5920           
  Branches     1346     1346           
=======================================
  Hits         5875     5875           
  Misses         44       44           
  Partials        1        1           

Impacted Files	Coverage Δ
src/ParseObject.js	99.89% <ø> (ø)

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[davimacedo]

Thanks for the PR! LGTM!